(a) Technical Field
The present disclosure relates to a battery's state-of-charge (SOC) balancing control method for a hybrid vehicle, in which the outside air temperature at a traveling destination is considered in determining an SOC strategy value.
(b) Background Art
Hybrid vehicles employ an electric motor as an auxiliary power source as well as an internal combustion engine to reduce exhaust gas and improvement fuel efficiency. The electric motor is driven by charge and discharge of a battery to increase the efficiency of a hybrid system (load leveling). Moreover, the battery is charged by regenerative braking during deceleration, in which the kinetic energy, which would be otherwise dissipated as frictional heat by a brake system, is converted into electrical energy by the power generation of the motor, thereby improving the fuel efficiency.
Various factors affect the fuel efficiency and driving performance of hybrid vehicles. One of the factors is the state-of-charge (SOC) of the battery.
The battery is an energy source for operating the motor of the hybrid vehicle and a DC/DC converter, and a battery controller monitors the voltage, current, and temperature of the battery and controls the overall SOC (%) of the battery. The operating point of the battery should be controlled such that the battery's SOC is maintained in a normal range and, if the battery's SOC is out of the normal range, it should be controlled to be restored to the normal range.
In an SOC band control of a high voltage battery, when the battery's SOC is lower than a preset value, the engine should be operated at an operating point higher than a desired power level to control the battery's SOC to charge orientation. On the contrary, when the battery's SOC is higher, the battery's SOC should be controlled to discharge orientation by increasing the amount of energy discharged from the electric motor.
A conventional SOC band control method of a high voltage battery is described with reference to FIGS. 3 and 4.
As shown in FIG. 4, the conventional SOC band control method includes a step of monitoring the current SOC value, a step of determining the orientation of the SOC value with a predetermined hysteresis, a step of determining an SOC strategy value based on the current SOC value, and a step of controlling the operating point of the vehicle based on the SOC strategy value.
For example, as shown in FIG. 3, the SOC strategy values are divided into critical low range 0 (SOC 0 to 25), low range 1 (SOC 25 to 40), normal range 2 (SOC 40 to 70), high range 3 (SOC 70 to 80), and critical high range 4 (SOC 80 to 100).
The SOC strategy value is determined based on the SOC value transmitted from a battery controller (BMS), and a hysteresis is determined such that the SOC strategy value is not suddenly changed by the current SOC value. That is, the hysteresis is predetermined such that the SOC strategy value is not suddenly changed by the current SOC value, and the orientation of the SOC value is determined by the predetermined hysteresis.
However, when the SOC strategy value is determined based on only the current SOC value, it is difficult to maintain the SOC strategy value in the normal range 2 in the event of a sudden change in the outside air temperature at a particular destination where it is expected to use an substantial amount of electricity by an auxiliary electrical load such as an air conditioner.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.